Update gpudb to v0.3.0

[singhpratech]

Updates gpudb to v0.3.0 (pinned ref moved to the release tag commit).

Highlights since the currently pinned v0.1.3:

• DOUBLE overloads for gpu_sum / gpu_min / gpu_max, alongside the existing BIGINT ones
• Native NULL semantics: empty input and all-NULL groups return SQL NULL
• DOUBLE min/max use the same NaN-aware total order as native DuckDB
• Streaming accumulator states — end-to-end queries through the SQL aggregates now run at parity with native DuckDB (1.00–1.20× on rewritten TPC-H queries)

Docs in description.yml are updated to match, including the known-limitations section.

Pre-validated on my fork with the standard build workflow — all four platforms green: https://github.com/singhpratech/community-extensions/actions/runs/30496129279

Thanks as always!